Electrically writable and erasable non-volatile memories can be realized with storage means comprising alterable resistive elements. Resistive memories have extensively been studied for device applications in the past. Especially many transition metal oxides have been shown to exhibit a memory switching mechanism, which can be activated by pulses of reasonably small voltages and currents. A transition metal oxide structure typically consists of a metal/insulator/metal layer scheme with noble metal electrodes and reactively sputtered or plasma-oxidized thin metal oxide layers.
In the paper by I. G. Baek, et al., “Highly Scalable Non-volatile Resistive Memory using Simple Binary Oxide Driven by Asymmetric Unipolar Voltage Pulses”, IEDM 2004, which is incorporated herein by reference, a device structure is described that comprises storage means formed from transition metal oxide of binary composition. A layer sequence comprising transition metal oxide is arranged within the intermetal dielectric between the metalization levels M0 and M1. The bitlines are arranged in the metalization level M1. The memory element is connected with a source/drain region of a transistor structure. The second source/drain region is connected with the ground potential.
In the paper by M. Kund, et al., “Conductive bridging RAM (CBRAM): An emerging non-volatile memory technology scalable to sub 20 nm”, in EEDM 2005, 31-5, which is incorporated herein by reference, a random access memory is described that makes use of a solid-state electrolyte. A chalcogenide layer, especially GeSe, is arranged between a bottom electrode of tungsten and a top electrode of silver. The switching mechanism is based on the polarity-dependent electrochemical deposition and removal of metal in a thin solid-state electrolyte film. The ON state is achieved by applying a positive bias larger than the threshold voltage at the oxidizable anode resulting in redox reactions driving Ag ions into the chalgogenide glass. This leads to the formation of metal-rich clusters, which form a conductive bridge between the electrodes. The device can be switched back to the OFF state by applying an opposite voltage, by which the metal ions are removed, so that the conductive bridge vanishes.